As described in JP2000-262545A (see FIG. 1), a conventional occludator comprises, e.g., a lower bow-shaped part where a lower jaw tooth mold is mounted, an upper bow-shaped part where an upper jaw tooth mold is mounted, and a joint for connecting the lower bow-shaped part and the upper bow-shaped part, so that an artificial joint movement such as opening/closing of the tooth molds is obtained and a state of occlusion is reproduced. The occludator is used in the treatment of the occlusion of upper and lower teeth and the fabrication of prostheses.
The joint described in the conventional document is configured such that a maxillary rotation axis (2), which is combined with the upper bow-shaped part and is circular in cross section, is placed from above at a sagittal condyle path tilt angle on a concave combined with the lower bow-shaped part. A plate spring (3) applies an urging force to prevent detachment. A target joint movement is intended to be reproduced by specifying the sagittal condyle path tilt angle.
JP11-28217A (see FIG. 4) describes another form of a conventional occludator. The joint of the occludator is constituted of a condyle (12) composed of a sphere which is mounted on a lower bow-shaped part and protrudes upward, and a condyle box (17) mounted on an upper bow-shaped part. An articular fossa (condyle path) is represented by a plane of the condyle box.
According to the occludator of the latter conventional example, a Benette lift mechanism (15) for lifting an upper jaw tooth mold, from the condyle, separately from the condyle box is provided on the lower bow-shaped part (base). Thus, with respect to the position of the lower jaw tooth mold which is faithfully and accurately mounted as in a state of a living body, reset can be arbitrarily made on the occludator to a lower jaw position diagnosed as the most suitable for a living body, so that a target joint movement is obtained.
In the conventional occludator, the theory of overcompensation reproduction is used. The configuration of the joint is devised and the joint is adjusted on the basis of the overcompensation theory. In the theory of overcompensation reproduction, by setting a condyle path regulating mechanism of the occludator to make movements slightly more than the temporomandibular joint movements of an actual living body, prostheses fabricated on the occludator readily make diastases during lateral movements in an oral cavity. With this theory, even on an occludator less capable of adjustment, moderate prostheses can be fabricated with just a few adverse actions.
However, some errors inevitably occur in mandibular movements reproduced by a semi-adjustable occludator which is less capable of adjustment. A prosthesis fabricated by such an occludator may cause an error which is collision with or separation from opposed teeth during lateral movements. Particularly when providing balanced occlusion for a full denture, a prosthesis may fail due to any of these errors.
Diastasis (right and left artificial teeth of a full denture occlude on a working side and separate on a balanced side) does not cause any problems when prostheses are fabricated for a few teeth. However, when a number of teeth are lost or in the case of a full denture, a stretch of the theory suggests that flat surfaces are better for the occlusion planes of artificial teeth, which may lead to misinterpretation. Flat occlusion planes have low mastication efficiency and cause an enormous load on alveoli and periodontia. Thus, flat surfaces are not always preferable. Rather than flat surfaces, the cusps of molars should be sharpened as much as possible.
In this sense, various kinds of average value occludators (an average value is used as a condyle path angle), semi-adjustable occludators, and totally adjustable occludators (although a condyle path angle can be personally adjusted, the adjustment is difficult and is not correct in a three-dimensional manner) are conventionally produced and prostheses have been fabricated by reproducing occlusion by means of the occludators.
Although various kinds of inventions are devised for joint movements on occludators as described in the conventional examples, the inventions are all based on a joint structure composed of a rod or sphere circular in cross section. An angle, a position, etc. are intended to be adjusted in compliant with the overcompensation theory to obtain joint movements required for prostheses but an actual joint shape is not intended to be reproduced. That is, as described above, dental care workers conventionally comply with the theory of overcompensation reproduction and have no idea about reproduction of an actual shape of a temporomandibular joint. This fact is evident from JP11-146889A which relates to an invention of an artificial temporomandibular joint. In this invention, an articular head is shaped like a rugby ball.
In this invention, a face bow is used to obtain an occlusion plane relative to a predetermined standard plane (e.g., a standard plane such as the Frankfurt plane and the Camper's plane) of a target patient and reproduce the plane on an occludator.
In the conventional face bow, for example, ear rods provided on the ends of right and left legs are inserted respectively into the external auditory meatuses of a patient, the body of the face bow is disposed on the predetermined standard plane, and the occlusion plane position of the upper jaw of the patient is obtained by a bite fork mounted on the face bow.
Then, the occlusion of an upper jaw tooth mold and a lower jaw tooth mold is positioned on the obtained occlusion plane, and the upper jaw tooth mold and the lower jaw tooth mold are mounted and reproduced on the corresponding occludator.
For example, in the case of an occludator with the Frankfurt plane, when the face bow is mounted on the patient, it is better to set the face bow on the Frankfurt plane. However, as described above, a joint of the occludator is constituted of a sphere and a platy member and thus the face bow does not have to be correctly positioned on the standard plane. According to the mechanism of the conventional face bow, it is difficult to correctly make setting on the standard plane. Thus, the face bow is not so correctly positioned on the standard plane in ordinary cases.
Moreover, the conventional face bow is made of a material not permitting the passage of X-ray beams, e.g., a metal.